Known building control or danger warning systems include a two-core circular bus to which bus users (e.g., alarm systems) are connected in parallel. In case of an interruption of the circular bus, two stub lines that may be operated independently from each other remain. In case of a short-circuit, the segment concerned may be disconnected by separate circuit breakers that are controlled by a central control station of the building control or danger warning system, so that, for example, shortened but operational stub lines still remain available.
In the following, the term “signal system” is used to include building control or danger warning systems.
In the course of assembly of signal systems of this kind, the bus users connected to the circular bus, and the circuit breakers, must be looped-into the circular bus. Bus users that are provided with polarity reversal protection and can be connected rapidly are known. However, the circuit breakers must be connected with correct polarities.
Color-coded conductors simplify the assembly of the circuit breakers only to a limited extent, because there is no world-wide uniform standard for color coding. Therefore time-consuming determination measurements on individual cores cannot be avoided, in particular when existing plants are being extended.
Furthermore, signal systems are known in which circuit breakers, usually in the form of relays or FETs (i.e., field effect transistors), are incorporated in the bus users. Bus users of this kind are connected in series into the circular bus, with care being taken to ensure correctness of polarity. Although the incorporation reduces the outlay of assembly work, it is still necessary to perform time-consuming determination measurements on the individual cores. Signal systems of this kind are known from DE 36 14 692 A1, DE 43 22 841 A1, CH 651 688 A5, and EP 468 097 A2.
A bus user circuit that is usable for a signal system of the generic kind as previously mentioned is known from DE 198 50 869 A1. This bus user circuit has two circuit breakers, each of which connects two cores of the circular bus. Therefore a bus user fed from both sides must be connected to the bus with the same designated polarity despite the polarity-reversal protection bridge, so that in this case too, determination measurements must be performed on the individual cores.